Investigation of different ways of activation of fly ash–cement mixtures

Cement industry emits large amount of CO2. One of the ways to reduce this emission is to use cement replacements, such as fly ash, in binding mixtures. Blends containing fly ash exhibit different properties compared to typical portland cement. In the case of very high amount of fly ash used as substitute of cement, setting and hardening are elongated, and early compressive strength and also often ultimate strength are reduced. Thus, such blends require activation. The aim of the work was to clarify the influence of chemical activators (Ca(OH)2 and Na2SO4 used together) on hydration/activation of fly ash–cement mixtures containing about 80% of fly ash. Activated mixtures containing inert filler instead of fly ash or cement were also investigated to better understand the influence of chemical activators on each component of the blend. The research included early hydration periods (3 and 24 h) and subsequent days (till 90th day of hydration). Several methods were used: calorimetry, TG/DTG, FTIR, X-ray diffraction and SEM microscopy.